Process for the preparation of furfural

ABSTRACT

The invention relates to a process for the preparation of furfural from a carbohydrate, comprising subjecting a lactose-containing material to steam distillation, whereby at least part of the lactose present is converted to furfural.

This is division of application Ser. No. 672,296 filed Mar. 31, 1976 nowU.S. Pat. No. 4,076,733.

The present invention relates to an improved process for the preparationof furfural from carbohydrates by steam distillation.

Although the discovery of furfural dates back to the early half of thenineteenth century there was still in 1920 no commercial production offurfural. By that time the Quaker Oats Company in nineteenhundred andtwentytwo started commercial production of furfural, the first importantuse thereof being for the production of phenolic resins. Other uses weredeveloped and the demands for furfural made necessary a considerableexpansion in production capacity due to i.a. the synthetic rubberprogram during World War II.

To-day furfural is commercially produced in great quantities, andpentosan-containing raw materials are used for such production. Typicalraw materials are corn cobs, bagasse, peanut hulls and also to someextent birch wood. Corn cobs are an abundant source and this is the mainraw material used in the production of furfural.

The manufacture of furfural is based on forming pentose from pentosanand water and hydrolyzing the pentose to yield furfural and water.Commercially, furfural is produced in a single-step operation.Basically, there are two different ways of producing furfural. In oneprocess, the raw material is treated with dilute sulphuric acid. Inanother process, acidic conditions are formed in situ when using birchwood as a raw material. The acid conditions arising in the latter caseare due to the formation of acetic acid.

In both processes, the furfural formed is removed by steam distillation.The vapours leaving the digesters are condensed and fed to a strippingcolumn, where the overhead vapours, rich in furfural, are condensed andcooled and generally separated into two layers. The furfural layercontaining about 6% water is sent to the dehydrating column, where thewater is taken overhead and dry furfural is drawn from the base.

One drawback of the furfural production technique as described above isthe fact that the raw materials used up to now contain a relatively lowpercentage of pentosans, which means that enormous quantities of rawmaterials have to be handled and treated to obtain the desiredquantities of furfural. Thus, the energy and apparatus requirements areextensive and result in relatively high production costs.

In accord with the instant invention, it has now surprisingly been foundthat, by using as a raw material a lactose-containing material,including lactose per se, furfural is obtained in a high yield. Thelactose or lactose-containing material may be used as such or may beadded to any other raw material of the conventional type, which resultsin a substantial increase in the yield of furfural.

The fact that lactose reacts in a manner to give furfural is in factsurprising, since as generally recognized lactose is a dihexosecontaining one galactose unit and one glucose unit. Generally, whentreated with acid, hexoses do not form furfural but rather derivativesthereof in view of the presence of a sixth carbon atom. It was thereforehighly surprising that steam distillation of lactose resulted in theformation of furfural in high yield.

In general, the yield will be seen better if the lactose is oxidizedunder mild conditions before or during the acid hydrolysis. Although theinvention is not to be bound by any theory, the reason for the improvedyield obtained by pre-oxidizing the lactose-containing material or thelactose per se may be the formation of a carboxyl group, which in turnsplits off carbon dioxide to form a five-carbon atom carbohydrate, whichthen in turn hydrolyzes to furfural in high yields.

For oxidizing the lactose to improve the yield of furfural any oxidatingagent capable of mild oxidation of organic compounds can be used,examples being bromine, aqueous hydrogen peroxide, dilute nitric acid,peracids, or the like. Among the peracids peracetic acid is preferred,although other peracids, such as perbenzoic and monoperphthalic, mayalso be used. It is immaterial whether the peracid is generated in situby addition of hydrogen peroxide to the carboxylic acid, or if theperacid is preformed. The pre-oxidation is preferably performed at anincreased temperature, such as up to about 80° C.

Any lactose-containing material can be used to form furfural accordingto the invention. Beside lactose per se, whey obtained from cheeseproduction is an excellent raw material, the lactose preferably in suchcase being used in the form of an about twenty percent by weightconcentrate of lactose in water. Such concentrate is readily obtained byremoving the milk protein from the whey and concentrating the lactosesolution thereby obtained. Generally, whey tends to constitute anenvironmental problem, since it is produced in great quantities inmilk-treatment plants all over the world, no practical use of the wheyhaving been found prior to the present invention.

The results of practical tests performed indicate that approximatelyhalf of the lactose molecule is converted in such a manner to givefurfural but, under most favourable conditions, a major part of thelactose seems to be convertible into furfural. For maximum yield it ispreferred to use an oxidating milieu under moderate acid conditions.

Accordingly, the main object of the invention is to provide a processfor the preparation of furfural from lactose or a lactose-containingmaterial by steam distillation alone or together with some otherinexpensive raw material containing pentosans, for example of the typeas indicated above in the introductory part of this specification.

Yet another object is to provide for a process whereby furfural isproduced in an increased yield while facilitating the raw-materialtreatment and decreasing the energy requirements.

Still another object is to provide a process for the preparation offurfural, starting from a wood material resulting in per se productionof acetic acid, with addition thereto of a lactose-containing material,either preceding or during the reaction but preferably also prior tocommencement of steam distillation of the wood material.

A further object of the invention is to provide a process for thepreparation of furfural by using a pre-oxidized lactose-containingmaterial as a starting material.

The invention will now be further described by specific examples which,however, must not be construed to delimit the scope of the invention.

In the following examples there is used a stainless steel reactor, tothe bottom of which there is introduced steam having a pressure of about12 atms and a temperature of about 186° C. The vapours leaving thereactor are transferred to a water-cooled condenser, the condensate fromwhich is analyzed with regard to its content of furfural. The analysisis carried out with a gas chromatograph of the type Perkin Elmer, ModelF17 (Perkin-Elmer Limited, England), pyridine in a known amount beingadded to the samples and used as a control reference. The raw materialsmay be introduced into the reactor through a removable upper end wall.

It is to be noted that the test reactor, used in performing thepractical experiments as per the following examples, is operated in abatch-wise manner, the residual hydrolysate being removed after eachtest. In each test the steam treatment had a duration of 1 hour and 45minutes, during which period the vapours leaving the reactor werecondensed and collected for gas chromatography to determine the furfuralcontent of the condensate.

EXAMPLE 1

5000 g of birch wood chips, having a dry solids content of 2690 g, aresupplied to the reactor and treated in the manner indicated above. Thecondensate is analyzed by gas chromatography with regard to its contentof furfural, the yield of furfural being 4.8% by weight on a dry basisof the birch wood. This test is used as a control test.

EXAMPLE 2

Birch wood chips in the same amount and of the same type as in Example 1are supplied to the test reactor together with 200 g of whey lactose inpowder form. Said materials are subjected to the same treatment as inExample 1, and upon analyzing the condensate the yield of furfural isfound to be 6.7% by weight on the same basis.

EXAMPLE 3

The procedure in Example 2 above is repeated, but in this case 170 mlaqueous 35% hydrogen peroxide solution are also added to the reactorbefore the steam treatment. The yield of furfural is 7.82% by weight onthe same basis.

From the above examples it can readily be seen how the lactose additioncontributes to the yield of furfural. It must, however, be noted thatthe basic furfural yield as per Example 1 above does not reflect thetrue yield in a continuous process for the preparation of furfural,since the acetic acid level of the test reactor starts at zero, whereasin a continuous process the acetic acid level builds up and becomesconstant at a certain level, which is favourable for a high furfuralyield. Therefore, in order to simulate the conditions of a continuousprocess, further experiments were performed as follows.

EXAMPLE 4

The procedure of Example 1 is repeated while adding also 125 ml ofglacial acetic acid to the reactor before closing same. The yield offurfural is 8.4% by weight on a dry basis of the birch wood.

EXAMPLE 5

Now Example 2 is repeated while adding the same amount of glacial aceticacid as per Example 4. The yield of furfural is 10.2% by weight on thesame basis.

EXAMPLE 6

The procedure of Example 1 is repeated while adding also 50 ml ofconcentrated sulfuric acid to the reactor before closing same. The yieldof furfural is 8.7 percent by weight on a dry basis of the birch wood.

EXAMPLE 7

Now Example 2 is repeated while adding the same amount of concentratedsulfuric acid as per Example 6. The yield of furfural is 10.5% by weighton the same basis.

EXAMPLE 8

The procedure of Example 3 is repeated while adding also 125 ml ofglacial acetic acid to the reactor before closing same. The yield offurfural is 10.9% by weight on a dry basis of the birch wood.

EXAMPLE 9

The procedure of Example 3 is repeated while adding also 50 ml ofconcentrated sulfuric acid to the reactor before closing same. The yieldof furfural is 11.1% by weight on a dry basis of the birch wood.

It is clear from the above examples that steam distillation underoxidizing conditions is favourable with regard to the overall yield offurfural. It is also clear from Examples 4 to 9 that the presence of anacid is favourable to the yield of furfural.

As has been indicated earlier in this specification, whey is an abundantmaterial found in all milk-producing spots of the world. Whey containsas major constituents lactose and protein, these constituents beingseparable by applying a so-called membrane technique. Up to the instantinvention, lactose has not found any wide-spread use. Against thisbackground this invention is of a far-reaching economical importance,since lactose may easily be added to the conventional raw materials inexisting plants for furfural production resulting in an improvedcapacity of the plant without significantly increased raw material cost.The lactose may be added in the form of a dry powder but can also beadded in the form of an aqueous concentrate, although in the latter casea somewhat increased steam consumption results.

It is to be understood that the invention is not delimited to the aboveexamples which are based upon the use of birch wood chips as a basicfurfural-producing raw material, and that it is equally applicable toall kinds of raw materials as indicated earlier in this specification.The process of the invention is thus useful also in connection withdigestion and treatment in the presence of dilute sulphuric acid orother mineral acids which have been used previously for such type ofproduction, albeit with somewhat lesser degree of economic advantage.

It is to be understood that the invention is not to be limited to theexact details of operation or exact compounds, compositions, methods, orprocedures shown and described, as many modifications and equivalents ofthe process illustrated in the foregoing will be apparent to one skilledin the art and may be made in the method and procedure of the presentinvention without departing from the spirit or scope thereof.

What is claimed is:
 1. A process for the preparation of furfuralcomprising subjecting a lactose-containing material essentially free ofmilk proteins to steam distillation under acidic conditions, whereby atleast part of the lactose present is converted to furfural, comprisingadding an oxidizing agent to said lactose-containing material.
 2. Aprocess according to claim 1 wherein the furfural thus produced isdistilled off and recovered.
 3. A process according to claim 1, whereinthe oxidizing agent is added to the lactose-containing material beforesteam distillation is commenced.
 4. A process according to claim 1,comprising adding the oxidizing agent to said lactose-containingmaterial during the steam distillation thereof.
 5. A process accordingto claim 1, wherein the oxidizing agent is hydrogen peroxide.
 6. Aprocess according to claim 3, wherein the oxidizing agent is hydrogenperoxide.
 7. A process according to claim 4, wherein the oxidizing agentis hydrogen peroxide.
 8. A process according to claim 1, wherein theacidic conditions are due to a non-oxidizing acid at least as strong asacetic acid.
 9. The process of claim 8, in which the acid is sulfuricacid or acetic acid.
 10. The process of claim 8, in which thelactose-containing material comprises a whey concentrate from which themilk proteins have been removed.
 11. The process of claim 10, in whichthe acid is sulfuric acid or acetic acid.
 12. In a process for thepreparation of furfural from a pentosan-containing raw material by steamdistillation under acid conditions, the improvement comprising adding tosaid raw material a lactose-containing material which is essentiallyfree of milk proteins whereby the yield of furfural in the vapoursdistilled off is substantially increased, and including the step ofadding to said raw material also an oxidizing agent.
 13. The process ofclaim 12, in which the acid conditions are due to a non-oxidizing acidat least as strong as acetic acid.
 14. The process of claim 13, in whichthe acid is sulfuric acid or acetic acid.
 15. The process of claim 12,in which the lactose-containing material comprises a whey concentratefrom which the milk proteins have been removed.
 16. The process of claim12, in which the pentosan-containing raw material comprises birch woodbark and the acid comprises acetic acid derived in the steamdistillation from said birch bark.
 17. The process of claim 16, in whichsulfuric acid is added.
 18. The process of claim 17, in which thelactose-containing material comprises a whey concentrate from which themilk proteins have been removed.
 19. A process according to claim 16,wherein the lactose-containing material is added to the birch woodbefore supplying steam thereto.
 20. A process according to claim 16,wherein the oxidizing agent is selected from the group consisting ofbromine, aqueous hydrogen peroxide, dilute nitric acid, and peracids.